1. Field of the Invention
The present invention relates generally to equipment for adjusting the tension in an endless element, such as a belt, entrained around a set of pulleys. More specifically, the present invention concerns an eccentric pulley shaft for carrying a pulley wherein shifting of the pulley shaft effects the tension in the belt or chain entraining the pulley—such as in a drive system for a centrifugal supercharger—without the need for an undesirable idler pulley.
2. Discussion of Prior Art
It is known in the art to utilize a set of pulleys or gears entrained by an endless element, such as a belt or chain, to transfer power between a drive shaft and a driven shaft. For example, it is known in the automotive industry to power one or more components off of the crankshaft of an engine using one or more belts entraining a set of pulleys. One such component typically powered off of the crankshaft is a blower for providing compressed induction fluid to the intake manifold of an internal combustion engine, such as a centrifugal supercharger.
These prior art drive systems are problematic and subject to several undesirable limitations. For example, all of these drive systems require the use of at least one idler pulley or gear entrained by each belt or chain for adjusting the tension in the belt or chain. An idler pulley or gear is typically a third component entrained by the endless element that is configured in a triangular arrangement with the drive and driven components. To adjust the tension in the belt or chain, the idler component is shifted. Idler pulleys and gears are undesirable, for example, they increase the friction and/or drag on the endless element, they decrease belt life by “backbending” the belt in a triangular configuration, they increase undesirable slippage of the belt with the requisite triangular setup, and they are part and labor intensive. When the drive system is used to power the impeller of a centrifugal compressor these problems are further magnified as the impeller is often accelerated very quickly and rotated at extremely high speeds. Such conditions are particularly prevalent in some superchargers. For example, in some superchargers, the impeller is accelerated in excess of 80,000 rpm in much less than a second. Therefore, any drive system utilized must be capable of withstanding high accelerations and velocities without permitting untoward movement of the impeller relative to the rotational axis. Accordingly, there is a need for an improved drive system that minimizes the need for undesirable idler pulleys or gears.